A drive-train system of a vehicle and a method for controlling the operation of a drive-train system of a vehicle of the type mentioned in the introduction are generally known. The generic drive-train system includes at least one internal combustion engine, which can be started with the aid of an electric machine which is able to be coupled to it with the aid of a clutch and is able to be controlled with the aid of an engine-speed controller. The two drive machines form what is called a hybrid drive. The concept of the hybrid drive is becoming ever more important in automotive technology because it provides fuel economy, a reduction in emissions as well as an improvement in the subjective driving experience. In addition to the internal combustion engine, the hybrid drive has at least one further drive source, which does not require fossil fuels for its operation. In the case at hand, the electric machine is used as additional drive source. A suitable operating strategy makes it possible to utilize the advantages of the different drive sources to optimum effect and to avoid any disadvantages. The combination of the internal combustion engine with the electric machine is the predominent development.
Vehicles having a hybrid drive have lower fuel consumption than conventional vehicles, i.e., vehicles driven exclusively via the internal combustion engine. The savings in consumption are due to the hybrid-specific options of what is referred to as energy recuperation during a braking operation, and the implementation of start-stop functions. In hybrid drives a differentiation is made between a parallel hybrid, a serial hybrid, and a split hybrid. All share the feature of using two energy stores, i.e., a battery and a fuel tank. Capacitors are also able to be used as an alternative to the battery. A further differentiating feature in hybrid drives is the capacity of the individually employed electric machine. In this context it is distinguished between a mild hybrid and a full hybrid, the full hybrid being a vehicle that is at least intermittently able to drive using the electric drive alone. So-called powersplit hybrid drives are not considered for the technical approach in the case in hand, since their startup operation takes a different course so that the problem underlying the exemplary embodiments and/or exemplary methods of the present invention does not arise. Furthermore, so-called starter generators are known whose electric machine is permanently connected to the crankshaft of the internal combustion engine, however, which means that the problem of the synchronization between the internal combustion engine and the electric machine is not an issue.